Phenotypes of Gtf2ird1Gt(XE465)Byg/Gtf2ird1Gt(XE465)Byg (B,F-H, M and N) Gtf2iGt(XE029)Byg/Gtf2iGt(XE029)Byg (C,D, I-K and O-Q) embryos at E9.5 - E12.5 (I-K). (B-D) Mutants are much smaller compared with a wild-type littermate (A), and some are resorbed. The morphology of the cranial region of mutants is distinct from that of wild-type littermates; they lack prominent mesencephalic and telecephalic vesicles. Homozygotes have a small first branchial arch (BA) and a reduced second BA. The dilated pericardial sacs are highlighted by arrowheads. (C) Malformation of the allantois in an E8.5 embryo is shown by a white arrow. The allantois appeared short and swollen and failed to fuse to the chorion in mutant embryos. Gtf2ird1Gt(XE465)Byg/Gtf2ird1Gt(XE465)Byg (F-H) and Gtf2iGt(XE029)Byg/Gtf2iGt(XE029)Byg (I-K) embryos showed open neural tube defects (exencephaly) and midfacial clefts (black arrow). The embryo in K has hemorrhaging in the head. The wild-type E10 embryo is shown in E. (L and M) Yolk sac angiogenesis defects in E10.5 Gtf2ird1Gt(XE465)Byg/Gtf2ird1Gt(XE465)Byg embryos. Gross morphology of yolk sac of wild-type and mutant embryos at E10.5. The mutant yolk sac exhibits a pallid appearance because of the vast reduction in circulating erythrocytes. Large blood vessels and extensive branching of the vessels can be seen in the wild-type yolk sac (black arrowhead in L), but there is absence of an organized yolk sac vasculature in the mutant embryo, although blood islands are readily detectable. (N-Q) Vascular defects in E10.5 and E12.5 Gtf2ird1Gt(XE465)Byg/Gtf2ird1Gt(XE465)Byg and Gtf2iGt(XE029)Byg/Gtf2iGt(XE029)Byg embryos. Mutant embryos with hemorrhage in the head, the neck and the pericardial cavity are shown by black arrowheads.